It is known to use various forms of collapsible and fold-up ladders for both domestic and commercial use. Many of these prior art ladders are very bulky when collapsed and could be extremely difficult to carry. Generally, these ladders require time-consuming and difficult processes for disengaging the ladder after use and are too bulky for easy storage. Correspondingly, most of these known ladders are troublesome to set up for use after storage.
Collapsible ladders on the market today consist of sections of several rungs which are almost of the same length as that of the main base strut or rung of the portable ladder itself. These struts or rungs are linked by clamps to the side rails between which the struts or rungs are placed.
These clamps secure the struts of the main and secondary sections allowing the extension of this secondary section from the main section. By pulling the secondary sections out from the main section along the clamps, the ladder is extended to its maximum width. These ladders are known as extension ladders and have a compacted size of at least the size of the main section. They are often difficult to extend and are even more difficult to compact.
Another design consists in linking both long sections, main and secondary on their ends by a hinged joint.
These ladders are not structurally secure and need to be of a length again no shorter than the length of the main section. Nevertheless, this second embodiment is less reliable for the use of the ladder, as the securing lugged nut at the hinges has to exert a great pressure in the aligned position in order to avoid the collapsing of the end of the ladder once it has been subject to the load of the person stepping on the additional top section. Therefore, this model is still less safe than the first. Nevertheless, both show the drawback of the difficulty of handling because of their weight and bulkiness. Neither configuration is small enough to fit into the trunk of a car, or can easily be stored in a garage or shed.
As noted above, the presently available ladders have serious drawbacks when assembling for use, or disengaging for storage. In addition, they are relatively expensive to manufacture and not always structurally reliable when in use.
Typical fold-up ladders are disclosed in U.S. Pat. Nos. 3,216,526; 3,554,318; 3,655,012; 3,730,295; and 3,811,151.
There are also known chain type or link fold-up fire escape ladders that are not rigid but rather are intended to be flexible when extended for use. These ladders are generally suspended from windows by a hook or chain and dangle from an escape portal or window so people can descend therefrom. None of these ladders are adapted to be locked in a rigid structure nor can any be used as an ordinary lean-to or stepladder. Typical escape ladders of this type are disclosed in U.S. Pat. Nos. 303,884; 308,179; 1,644,739; 2,529,112 and in British Pat. No. 433,724 dated Aug. 20, 1935.